Passive harmonic filter power quality monitor and communications device
A method and apparatus for detection of a failure of a rectifier connected to a passive harmonic filter with a tuned circuit reactor, or of the filter itself, using low cost voltage sensing, modeling of reactor resistance and saturable inductance, and a mathematical integration. The harmonic spectrum of the rectifier current is used to determine an estimate of the rectifier impedance. A template of expected rectifier current is calculated, and compared against a rectifier current calculated on the basis of sensed voltages, to generate a difference signal. The difference signal is compared against a predetermined fault threshold to determine if an error has occurred. The apparatus includes a DSP obtaining the voltages of the source and load, and the tuned circuit reactor voltage, and configured to compare the currents calculated from the actual voltages with the currents in the template, and to thereby determine whether to annunciate a fault.
1. A monitoring device for application to a passive harmonic filter connected to a source and to a load, the passive harmonic filter having a line reactor with inductor taps, the line reactor connected between the source and the load, the passive harmonic filter further having a tuned circuit reactor and a tuned circuit capacitor connected in series with each other and parallel to the line reactor, the monitoring device comprising:
a digital signal processor;
a connector connected between the digital signal processor and the source, to enable the digital signal processor to obtain a voltage at the source;
a connector connected between the digital signal processor and the inductor taps of the line reactor, to enable the digital signal processor to obtain a voltage at the inductor taps;
a connector connected between the digital signal processor and a node between the tuned circuit reactor and the tuned circuit capacitor to obtain a voltage across the tuned circuit reactor; and
annunciation means by which the digital signal processor announces a failure of the passive harmonic filter in the event that the digital signal processor determines the existence of the failure.